Integrated communications and power system

ABSTRACT

In order to avoid signal disturbances at communications through electric high power cables for supply of electric power to offshore installations, power cables that are galvanically insulated from each other are used. For example this may be done by supplying power at two single-phase pairs and use one conductor in every pair as signal conductor or by using a three-phase cable plus a single conductor.

RELATED APPLICATIONS

This application claims priority to Norwegian Patent Application20022909 filed Jun. 17, 2002 and claims the benefit of PCT ApplicationSer. No. PCT/NO03/00199, filed Jun. 16, 2003, which are incorporatedherein in their entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a system that combines transmission ofpower and signals via a custom designed cable configuration to offshore,especially subsea located control units.

BACKGROUND OF THE INVENTION

To reduce the outlet of carbon dioxide and other environmentallyunfriendly gases, the authorities have encouraged and imposed a supplyof electrical power from onshore power plants to offshore installations.For a subsea installation a power supply via a cable from land isusually the only possibility.

In addition to the power supply offshore installations are more and moredependent on data communication with land based facilities. Subseainstallations may be fully controlled from land. This requires a largeamount of data to be sent between the installation and land.

The principle of simultaneously utilizing power transmission cables andlines for communication purposes is commonly known under the terms“comms-on-power” or PLC (Power Line Carrier). Onshore this has beenperformed since long ago. Offshore it is typically applied as supplementto optical fiber cable, but may also be installed as the only system.Installed as the only system it has certain technical advantages, e.g.it may reduce the number of subsea wet mateable connectors required. Thepower and communications is subsequently distributed to each controlunit.

Over very long distances—typically above 100 km—a combined power supplyand signal communication is very difficult and the signals are subjectedto disturbance from the electric current. On shore this can be solved byinserting amplifiers at certain intervals. Offshore amplifiers are notdesired, since this would mean installing delicate equipment at theseabed where access for maintenance is extremely difficult.

BRIEF SUMMARY OF THE INVENTION

The present invention aims to solve this problem without or at leastwith a substantially reduced need for amplification of the communicationsignals.

The invention provides overall system design considerations andimplementations that have been made to achieve and optimize the abovedescribed dual functionality by utilizing a set of, preferably, fourcopper conductors for both power and communication signal transfer.

A further advantage of the present invention is that utilization of twoconductor pairs introduces redundancy and robustness both with respectto power supply and communication, enabling continued operation of theICPS (Integrated Communications and Power System) after the occurrenceof a single failure.

One embodiment of the present invention is an Integrated Communicationand Power System, comprising at least one first transformer located onshore, at least one second transformer located offshore, with at leastfour single conductors connecting the first transformer with the secondtransformer, wherein at least four of those single conductors conductelectric power and communication signals. Four of these singleconductors are arranged in pairs and conduct electric power, the pairsbeing galvanically insulated from each other, and the communicationsignals being conducted in one conductor of at least one pair. Filtersare coupled to the first transformer and the second transformer.

The features and advantages described herein are not all-inclusive and,in particular, many additional features and advantages will be apparentto one of ordinary skill in the art in view of the drawings,specification, and claims. Moreover, it should be noted that thelanguage used in the specification has been principally selected forreadability and instructional purposes, and not to limit the scope ofthe inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail under reference to theaccompanying drawings illustrating embodiments of the invention, inwhich:

FIG. 1 shows a first embodiment in a so-called quad arrangement,

FIG. 2 shows an alternative embodiment in a 3 phase plus single cablearrangement,

FIG. 3 shows schematically a cross section through a cable implementingthe arrangement for FIG. 1,

FIG. 4 shows schematically a cross section through a cable implementingthe arrangement for FIG. 2, and

FIG. 5 shows schematically a transformer to be used with the arrangementof FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Two alternative ways of arranging the conductors are shown in FIGS. 1and 2, respectively; FIG. 1 showing a quad system with two pairs ofconductors and FIG. 2 showing a three phase arrangement with anadditional single conductor. In both alternatives the connections arearranged and connected in an unusual way to obtain the desired ICPSsystem optimum. The 3 phase+1 conductor system can be used for longerdistance than the quad in the cases where the cable insulation has anouter semiconductor.

As illustrated in FIGS. 1 and 2, the ICPS power is supplied at theonshore/topside end 1 and extracted at the subsea end 2 viamulti-winding, load-balancing transformers 3 and 4.

In the embodiment of FIG. 1 the transformer 3 has a primary winding 5and two secondary windings 6 and 7. The secondary windings are connectedto a respective pair of conductors 8, 9 and 10, 11. Each of thesecondary windings 6, 7 is equipped with a filter 12. The transformer 4has two primary windings 13 and 14 and a plurality of secondary windings15. Each of the primary windings 13, 14 and each of the secondarywindings 15 is equipped with a filter 12.

The secondary windings 15 distribute power and signals to the variousequipment on the installation.

In the embodiment of FIG. 2 the transformer 3 has three phase primarywinding 16 and a three phase secondary winding 17. The three phasesecondary winding 17 is connected to three conductors 18, 19 and 20. Inparallel to the three conductors 18, 19, 20 is a single conductor 21. Ateach end of the conductors 18–21 is a filter 12.

The transformer 4 has a three phase primary winding 22 and a pluralityof single phase secondary windings 15. Each of the secondary windings isequipped with a filter 12. As for the embodiment of FIG. 1, thesecondary windings 15 are distributing power and signals to the variousequipment on the installation.

FIG. 3 show schematically a cross section through the cable containingthe conductors 8–11 in FIG. 1. In this FIG., 1L1 and 1L2 denotes the twoconductors 8 and 9 respectively, and 2L1 and 2L2 denotes the twoconductors 10 and 11, respectively.

FIG. 4 shows schematically a cross section through a cable containingthe conductors 18–21 in FIG. 2. In this figure L1, L2 and L3 denote theconductors 18, 19 and 20, respectively, and S denotes the singleconductor 21.

The conductors are preferably integrated in a common cable, like the onedescribed in Norwegian Patent Application No. 20020781, incorporated inits entirety by reference.

FIG. 5 shows schematically a transformer useful as the transformer 4 inFIG. 1. The transformer comprises an iron core 23, a first primarywinding 13, a second primary winding 14 and a plurality of secondarywindings 15.

The function and characteristics of the ICPS can be described asfollows: Fixed frequency power for energizing and operation of subsealocated control and communication devices is supplied to the primarywinding. The connection of the power is different from the connection ofthe comm's on power.

a) quad: The fixed frequency power is transferred on two insulatedcopper conductor pairs contained in a single cable. Each pair issupplied from a dedicated power transformer winding, meaning that thetwo pairs are galvanically separated from each other. A filter forinsertion of the communications signals is connected in-between eachtransformer winding and conductor pair.

b) 3+1: Power is supplied as a standard 3 phase supply. A separate coresolely used for the comms' on power system forms part of the umbilical.

Transfer of communication signals within a designated frequency band isvia the same set of conductors used for power transmission in the quadembodiment and via the single conductor in the 3+1 embodiment.

Power and communication signals are separated at both cable ends bymeans of termination to custom designed filters.

The cable leading from an onshore or topside located power source isconnected to a custom designed, multi-winding power transformer at itssubsea located end.

a) For the quad: An integrated power and signal cable having fourinsulated copper conductors in fixed radial position relative to eachother along the full length of the cable, as illustrated by thecross-section in FIG. 3. The conductors are operated in pairs asindicated, both with respect to power supply and communications signals.The signals use one conductor in each pair, thus using galvanicseparated signal conductors with minimum interference of the signal.

b) For the 3+1: As illustrated by the cross-section in FIG. 4 the singlecore is not located close to the 3 cores used for the power supply. Thedistance between the single core and the 3 power cores is determined bya number of factors such as: minimum umbilical outer diameter, minimumcapacitance, and minimum inductance. The advantage is that the distancebetween the 3 cores and the standalone core can be varied, thusinductance for the comms system can be optimized.

The subsea multi-winding transformer design illustrated by FIGS. 1 and 2ensures that all subsea located control units are galvanicallyseparated, and thus that the consequences of a single fault is limitedto the faulty consumer.

-   -   a) For the quad: The split primary winding connections, winding        1 marked 1L1, 1L2 and winding 2 marked 2L2, 2L1 (see FIG. 5),        means that any control unit can be fed from either power        transmission conductor pair, thus limiting the effect of a        single failure to any one of these pairs. (In the traditional        case of a single primary winding and parallel connected power        transmission conductor pairs, this robustness would be lost.)

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto.

1. Integrated communication and power system, comprising: at least onefirst transformer located on shore, at least one second transformerlocated offshore, at least four single conductors connecting the firsttransformer with the second transformer, said at least four singleconductors conducting electric power and communication signals, whereinfour of said at least four single conductors are arranged in pairs, saidpairs being galvanically insulated from each other, and thecommunication signals being conducted in one conductor of at least onesaid pair, and wherein first transformer filters are coupled to saidfirst transformer and second transformer filters are coupled to saidsecond transformer.
 2. The system according to claim 1, wherein the atleast four single conductors form at least two pairs in a double singlephase quad arrangement.
 3. The system according to claim 1, wherein saidat least four single conductors are in a substantially fixed radialposition relative to each other in a length of a cable.
 4. The systemaccording to claim 1, wherein said second transformer has a plurality ofsecondary windings.
 5. The system according to claim 4, wherein saidplurality of secondary windings of said second transformer each have afilter.
 6. The system according to claim 4, wherein an offshore controlunit is fed from said secondary windings.
 7. The system according toclaim 1, wherein said communication signals are conducted from oneconductor in each of said pairs.
 8. The system according to claim 1,wherein said at least four single conductors are insulated copper linesand integrated into a subsea cable.
 9. A power and communications systemfor offshore installations, comprising: an onshore power andcommunication installation coupled to an onshore multi-windingload-balancing transformer; an offshore power and communicationinstallation coupled to an offshore multi-winding load-balancingtransformer; at least one control unit coupled to said offshoremulti-winding load-balancing transformer; a plurality of singleinsulated conductors housed within a core and coupled on a first end tosaid onshore multi-winding load-balancing transformer and coupled on asecond end to said offshore multi-winding load-balancing transformer,wherein said single insulated conductors housed within a core conductspower; at least one single insulated conductor proximate said core andcoupled on a first end to said onshore power and communicationinstallation and coupled on a second end to said offshore power andcommunication installation, wherein said at least one single insulatedconductor conducts communications; and wherein said plurality of singleinsulated conductors housed within a core and said at least one singleinsulated conductor proximate said core form a subsea cable.
 10. Thesystem according to claim 9, wherein said onshore multi-windingload-balancing transformer comprises an onshore multi-phase primarywinding and an onshore multi-phase secondary winding.
 11. The systemaccording to claim 10, wherein each of said onshore multi-phasesecondary windings has a filter.
 12. The system according to claim 9,wherein said offshore multi-winding load-balancing transformer comprisesan offshore multi-phase primary winding and a plurality of offshoresingle phase secondary windings.
 13. The system according to claim 12,wherein each of said offshore single phase secondary windings has afilter.
 14. The system according to claim 12, wherein each said offshoremulti-phase primary winding has a filter.
 15. The system according toclaim 9, wherein there are three single insulated conductors housedwithin said core forming a three phase power connection.
 16. The systemaccording to claim 9, wherein a radial distance between said singleinsulated conductor and said plurality of single insulated conductorshoused within a core is optimized for communications.